Super-bright
glow-in-the-dark paints
Discussion with pictures about a new type of paint that glows in the
dark and is ten times brighter than normal phosphorescent paints

Three things always bring a smile to the faces of children, and
adults who still have the joy of youth: soap bubbles drifting on a
breeze, helium-filled balloons, and things that glow in the dark. Of
these three, the last is the most mysterious and regrettably, many
times disappointing because whatever it is that is glowing, isn't
glowing very brightly... but not any more!

All of the glow-in-the-dark paints available in hobby and
party-supply stores use zinc sulfide-based phosphorescent pigments in
an acrylic medium. These paints were developed in the 1970s and glow
with a weak, yellow-green light. Occasionally, colored paints can be
found but these are even dimmer because the colored pigments added to
create the color block and absorb most of the light. Also, the
acrylic medium is so thick it's difficult to get an even coat. The
result is a weak, uneven glow. BUT, then someone discovered a new formulation!

Industrial-strength glow-in-the-dark paints use strontium (the
non-radioactive type) based pigments that glow ten times brighter and
last ten times longer than zinc-sulfide pigments. At least that's
what the advertisements claimed when I discovered them during an
Internet search. It sounded too good to be true so I ordered small
bottles of six different colors and tested them against some of the
regular paint obtained from the craft section of a Jo-Ann's Fabric
store. These high-end paints cost $20.00 per ounce or about eight
times the cheap stuff and were developed in the 1990s. Is it worth
the cost? Rather than simply state the results of my tests I thought
it would be more entertaining to take pictures of the tests, post
them on this page and let visitors judge for themselves. Here they are:

The first test compares the brightness of several different
thicknesses of paint using regular zinc-sulfide paint (bottom three
squares) versus the super-phosphorescent paint (top squares). The
bottom right square is one coat, the middle two coats, and the left
square three coats. The brightness of the regular paint in the lower
left square (three coats) is one-third the brightness of the
super-bright paint in the upper right square (one coat). This shows
that the strontium-based paint is vastly brighter than the
zinc-sulfide. Is it ten-times brighter? It was hard to tell when I
did this test because the light from the top row was so strong it
washed out the glow from the bottom row. This picture doesn't due
justice to how bright the strontium paint is glowing. A
two-inch-by-two-inch square glows as brightly as a .03 watt
electroluminescent night light. This glow paint casts shadows in a
dark room. You can read easily with it. No, it's not like a
flashlight but compared to normal glow-in-the-dark paints, this stuff
will knock your socks off... which you'd be able to find because it
glows brightly enough for you to see them... unless they ended up
under the bed... or you were standing on them... or... oh, well...
you get the idea.

The second test was to see the effect of backing material on the
brightness. The right-hand rectangle was painted on flat black paper.
The middle rectangle was on the shiny side of aluminum foil, and the
left-hand rectangle on white poster board. I had expected that the
black backing would be dimmer but was surprised by how much darker it
turned out to be. I thought the foil backing would be the brightest
but it was slightly dimmer than the white-backed rectangle. If you
paint any of these paints on to poster board, be sure to paint on the
shiny side of the board. If the paint is on the dull side, it will be
absorbed into the cardboard, make the cardboard translucent, and
weaken the glow because light will escape out through it. Also,
poster board may look opaque but it isn't, a lot of light leaks out
through the back and is wasted. The glow's brightness can be
increased slightly by giving the poster board a coat of
one-coat-covers-everything type gloss white paint. Even though the
paint is many times thinner than the poster board, it is much more
opaque and will reflect more light back out through the
glow-in-the-dark paint.

Here are the six colors I purchased. From left-to-right:
yellow-green, orange, turquois, violet (looks more like purple in
real life than the blue shown here), blue, and red. The red is dim
because it was only available in a colored pigment, which means that
much of the radiated light is absorbed by the coloring. Orange was
very disappointing. I had expected that it would have been brighter
because orange is close to yellow. In truth, it looked more like
brown. I should point out that with the exception of red, these
paints all glow in the color seen. They aren't glowing with white
light that is colored by pigments in the medium.

I did a time-to-charge test. Glow-in-the-dark paints work by
absorbing white light and them emitting it slowly in one color. They
are sort of like rechargeable batteries: before you get anything out
of them you have to put something in. And just like a battery, it
takes time to charge the paint up. Exposing samples for ten minutes,
five minutes, two minutes, one minute and thirty seconds generated
glows that all looked to be equally bright, but two hours later the
sample that had charged for ten minutes was twice as bright as the
one that only charged for thirty seconds. This test only used a
single heavy coat of paint. A sample with many coats might take
longer to become fully charged.

Another interesting test compared the charging times for strontium
and zinc-sulfide paints. For charging periods under twenty seconds,
the zinc-sulfide glowed brighter than the strontium paint. At twenty
seconds they were equal and after that the strontium paint's
brightness greatly out-glowed the zinc-sulfide.

Speaking about how long the the paints glow, the strontium paint is
clearly visible eight hours later. The zinc-sulfide paint faded to
oblivion in fifteen minutes.

One catch to using the strontium-based paints is that the pigment is
much heavier than the lacquer medium used to carry it. This means
that the pigment settles quickly and regular stirring in necessary. I
found that I had to stir the bottle every five minutes to keep it
even. Also, after sitting on a shelf for a day, the pigment packs
down in the bottom of the jar so densely that it's difficult to
getting it broken up and back into suspension. It helps to set the
bottle upside down for ten minutes to let the pigment start falling
away from the bottom before stirring. That way there is less chance
of some of the pigment crystals being damaged from being dug out of
the bottom of the bottle.

My next project involved attempting to increase the brightness of
the glow by increasing the amount of glowing pigment in the paint.
Typically, only thirty percent of the paint (by weight - it looks
much less than this by volume) is pigment, a fine granular material,
that glows. It would seem that if there was more pigment and less
binder, the paint should glow brighter. Also, using a super-super
phosphorescent paint (still based on strontium but with a larger
grain size, which is supposed to make it glow twelve percent
brighter) should also help. My first attempt used ninety-five
percent, by weight, of pigment and only five percent binder. This
mixture formed a very dry paste similar in texture to a very dry pie
dough. It was so dry that it had to be pressed into place. It did
glow slightly brighter and the glow lasted longer than the
ready-mixed paint, but not enough to make up for the hassle of the
mixing and pressing. Also, the mix was so dry that some pigment
crystals were damaged. These didn't glow and they made the surface
look as if it had a scattering of dark grains on it. It would seem
that a mixture of sixty percent pigment and forty percent binder is optimal.

I found that the type of paints I used were extremely slow drying:
it took days. When I tried speeding things up by placing a sample in
the sun on a cool day, the paint formed a network of small bubbles
just under the surface. These bubbles dulled the glow. When the paint
finally dries, it is still very flexible, whereas the cheap acrylic
paint hardened to a layer that cracks when bent.

So, do super-phosphorescent paints work enough better than the
hobby-shop stuff to warrant the additional cost? In my book, yes.
They are so much brighter and last so much longer that there simply
isn't any comparison. Also, the medium used by the company that
supplied my paints was smoother and more flowing than the hobby-store
acrylic paint so that after being brushed on, it flowed to an even
thickness. One problem I ran into while trying to paint very thick
coats is that the pigment would settle to the bottom of the layer of
paint just like it does in the bottle. This results in a thick layer
of dry medium on top of the pigment, with the result that the glow is
dimmed. The solution to this would be to increase the ratio of
pigment to medium.

How
Phosphorescent Paints Work:

Fluorescent
paints are paints that glow only when irradiated by an energy
source. A good example is the phosphor lining on the inside of a
fluorescent tube. Current flowing through mercury vapor inside the
tube creates ultraviolet rays that strike the phosphor. These
ultraviolet rays knock the electrons around the phosphor atoms into
higher orbits. The electrons immediately fall back down releasing the
energy they absorbed from the ultraviolet rays as visible light.

Phosphorescent
paints function in much the same way, except that once a light ray
bumps an electron into a higher or more energetic orbit the electron
gets stuck there. It's rather like a ball getting stuck in one of the
traps in a pinball machine. It stays put until the plunger underneath
the trap pushes it out so it can drop down to the bottom of the
table. The temporary entrapment is called a metastable state. In the
case of phosphorescent paints, what nudges the electrons out of the
energy trough that has them trapped is random thermal fluctuations in
the crystal structure of the pigment. This is why phosphorescent
paints glow weaker but longer when cold and brighter but shorter when
hot. An easy way to demonstrate this is to get some phosphorescent
glowing and press it with your thumb for a few seconds. The area
under the thumb will be heated and when the thumb is removed, will
glow slightly brighter than the surrounding cool area.

The
bright zone in the center, overexposed to white, is whereI
placed my thumb to warm an area and make it glow brighter.

The
color of the light released from a phosphorescent paint depends on
the difference between the energy levels of the trough the electron
gets trapped in and the ground state it falls to after being bumped
out of the trough. If this energy difference is high, the color will
be bluish. Mid-range energy differences show up as green or
yellow-green, and low energy differences as orange or red. This is
simply because a blue photon has more energy than a red photon.

In
2000 new zinc-based phosphorescent paints were developed that
radiate red and orange light instead of the traditional yellow-green.
Additionally, they are twice as bright as the older zinc sulfide paint.

IMPORTANT
UPDATE!!!

The
following video update shows what has changed in the world of
glow-in-the-dark paints since this page was created:

Both gentlemen I spoke to at Shannon were very patient and helpful
and while their company is geared more for industrial quantities,
were more than happy to supply small quantities at reasonable prices.

Great
New Link!!! I
found the following site to be very interesting and informative: http://www.glowinc.com.
They also seem to have very good prices.